Looking for clever ideas here....

Mac sending iTunes to Airport Express, Airport Express optical out to a Cambridge DAC, analogue signal from the DAC box into the Beocenter 2 amp using A.Aux, plays fine. Becentre 2 amp connected via Masterlink to Beolink Wireless 1 to send to additional speakers in the kitchen. Cannot get the A.Aux signal across the Wireless 1 Beolink.

Any clever ideas?

Unfortunately, the masterlink is not designed to access A.AUX over the link.  In some cases it works but if you ask B&O the answer is "it doesn't work"

There may however be a software update at some point to allow the A.AUX command to be reccognised.  You could try and trick the system though buy starting A.AUX in the main room, then manually swithing on the link speakers via the IR sensor and it will then play whatever is playing at that time ie. V.AUX.